<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>p4_居中测试</title>
    <style>
        *{
           margin: 0;
           padding: 0;
        }
        .main{
            background-color: #ff0;
        }
        .card{
            width: 200px;
            height: 300px;
            background-color: pink;
            border: 3px solid #f00;
            text-align: center;
            line-height: 300px;
        }
        .center{
            width: 1000px;
            background-color: lime;
            margin: 0 auto;
        }
    </style>
</head>
<body>
         <div class="main">
             <div class="center">
                 <div class="card">我是内容</div>
                 <div class="card">我是内容</div>
                 <div class="card">我是内容</div>
                 <div class="card">我是内容</div>
             </div>
         </div>
</body>
</html>